Active replication switch

ABSTRACT

A method, system, and computer program product for replication comprising allowing a subset of sites, wherein the sites comprise a first site, a second site and a third site and further wherein each site has a volume, to have active/active VSL replication, which presents two volumes at two different sites as a single volume, and another set of the sites to have a volume which is a replications of the volume presented by the VSL, and enabling the system to transparently shift which subset of the sites are replicated by the VSL and which sites are replications of the volume presented by the VSL; where the replication of the VSL is performed by a second replication technique.

A portion of the disclosure of this patent document may contain command formats and other computer language listings, all of which are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No. 13/434,620 filed on Mar. 29, 2012 now U.S. Pat. No. 9,037,818, the content and teachings of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

This invention relates to data replication.

BACKGROUND

Computer data is vital to today's organizations, and a significant part of protection against disasters is focused on data protection. As solid-state memory has advanced to the point where cost of memory has become a relatively insignificant factor, organizations can afford to operate with systems that store and process terabytes of data.

Conventional data protection systems include tape backup drives, for storing organizational production site data on a periodic basis. Such systems suffer from several drawbacks. First, they require a system shutdown during backup, since the data being backed up cannot be used during the backup operation. Second, they limit the points in time to which the production site can recover. For example, if data is backed up on a daily basis, there may be several hours of lost data in the event of a disaster. Third, the data recovery process itself takes a long time.

Another conventional data protection system uses data replication, by creating a copy of the organization's production site data on a secondary backup storage system, and updating the backup with changes. The backup storage system may be situated in the same physical location as the production storage system, or in a physically remote location. Data replication systems generally operate either at the application level, at the file system level, or at the data block level.

Current data protection systems try to provide continuous data protection, which enable the organization to roll back to any specified point in time within a recent history. Continuous data protection systems aim to satisfy two conflicting objectives, as best as possible; namely, (i) minimize the down time, in which the organization production site data is unavailable, during a recovery, and (ii) enable recovery as close as possible to any specified point in time within a recent history.

Continuous data protection typically uses a technology referred to as “journaling,” whereby a log is kept of changes made to the backup storage. During a recovery, the journal entries serve as successive “undo” information, enabling rollback of the backup storage to previous points in time. Journaling was first implemented in database systems, and was later extended to broader data protection.

One challenge to continuous data protection is the ability of a backup site to keep pace with the data transactions of a production site, without slowing down the production site. The overhead of journaling inherently requires several data transactions at the backup site for each data transaction at the production site. As such, when data transactions occur at a high rate at the production site, the backup site may not be able to finish backing up one data transaction before the next production site data transaction occurs. If the production site is not forced to slow down, then necessarily a backlog of un-logged data transactions may build up at the backup site. Without being able to satisfactorily adapt dynamically to changing data transaction rates, a continuous data protection system chokes and eventually forces the production site to shut down.

SUMMARY

A method, system, and computer program product for replication comprising allowing a subset of sites, wherein the sites comprise a first site, a second site and a third site and further wherein each site has a volume, to have active/active VSL replication, which presents two volumes at two different sites as a single volume, and another set of the sites to have a volume which is a replications of the volume presented by the VSL, and enabling the system to transparently shift which subset of the sites are replicated by the VSL and which sites are replications of the volume presented by the VSL; where the replication of the VSL is performed by a second replication technique.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of embodiments disclosed herein may be better understood by referring to the following description in conjunction with the accompanying drawings. The drawings are not meant to limit the scope of the claims included herewith. For clarity, not every element may be labeled in every figure. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments, principles, and concepts. Thus, features and advantages of the present disclosure will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 is a simplified illustration of a data protection system, in accordance with an embodiment of the present disclosure;

FIG. 2 is a simplified illustration of a write transaction for a journal, in accordance with an embodiment of the present disclosure;

FIG. 3 is a simplified illustration of sites with a virtual service layer, in accordance with an embodiment of the present disclosure;

FIG. 4 is an alternative simplified illustration of a virtual service layer with an I/O splitter, in accordance with an embodiment of the present disclosure;

FIG. 5 is a simplified illustration of an implementation of a virtual service layer, in accordance with an embodiment of the present disclosure;

FIG. 6 is a simplified illustration of an implementation of a virtual service layer with a splitter and recovery appliance, in accordance with an embodiment of the present disclosure;

FIG. 7 is a simplified illustration of an implementation of two sites with a virtual service layer, splitters and recovery appliances, in accordance with an embodiment of the present disclosure;

FIG. 8 is a simplified illustration of an implementation of two sites with a virtual service layer, splitters and recovery appliances and a mirrored volume, in accordance with an embodiment of the present disclosure;

FIG. 9 is a simplified illustration of an implementation of two sites with a virtual service layer, splitters and recovery appliances and a mirrored volume, CDP replica copies, journals, and repositories, in accordance with an embodiment of the present disclosure;

FIG. 10 is a simplified method of splitting I/O, in accordance with an embodiment of the present disclosure;

FIG. 11 is a simplified illustration of an implementation of two sites with a virtual service layer and splitters, in accordance with an embodiment of the present disclosure;

FIG. 12 is a simplified illustration of an implementation of two sites with a broken virtual service layer and splitters, in accordance with an embodiment of the present disclosure;

FIG. 13 is a simplified illustration of an implementation of two sites with data protection appliances and splitters, in accordance with an embodiment of the present disclosure;

FIG. 14 is a simplified method transitioning two sites from a virtual service layer for replication to using splitters and replication appliances for replication, in accordance with an embodiment of the present disclosure;

FIG. 15 is a simplified illustration of an implementation of two sites with data protection appliances, splitters, a virtual service layer and a bitmap, in accordance with an embodiment of the present disclosure;

FIG. 16 is a simplified illustration of an implementation of two sites with a virtual service layer and splitters, in accordance with an embodiment of the present disclosure;

FIG. 17 is a simplified method transitioning two sites from using splitters and replication appliances for replication to using a virtual service layer, in accordance with an embodiment of the present disclosure;

FIG. 18 is a simplified illustration of an implementation of two sites with a virtual service layer and splitters replicating IO to two other sites, in accordance with an embodiment of the present disclosure;

FIG. 19 is a simplified method transitioning two sites from using a virtual service layer and replicating to two other sites to using replication, in accordance with an embodiment of the present disclosure;

FIG. 20 is a simplified illustration of an implementation of two sites with a virtual service layer being broken, and splitters replicating IO to two other sites, in accordance with an embodiment of the present disclosure;

FIG. 21 is a simplified illustration of an implementation of two sites splitters replicating IO to another, in accordance with an embodiment of the present disclosure;

FIG. 22 is a simplified illustration of an implementation of two sites with a virtual service layer being established, and splitters replicating IO to two other sites, in accordance with an embodiment of the present disclosure;

FIG. 23 is a simplified method transitioning two sites from and replicating two other sites using replication to using a virtual service layer, in accordance with an embodiment of the present disclosure;

FIG. 24 is an example of an embodiment of an apparatus that may utilize the techniques described herein, in accordance with an embodiment of the present disclosure; and

FIG. 25 is an example of an embodiment of a method embodied on a computer readable storage medium that may utilize the techniques described herein, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

In some embodiments, the current disclosure may enable seamlessly transferring between replication (journal based or other) between two sites to active/active virtualization of data at the two sites. In certain embodiments, there may be multiple sites or replication appliances replicating one or more active production sites. In certain embodiments, the active sites may be synchronized by a virtual service layer. In certain embodiments, the virtual service layer may enable the active sites to contain the same data on each site. In some embodiments, the replication sites may asynchronously replicate the active sites to back-up the data on the active sites. In other embodiments, due to resources and other constrains not all site may be active at the same time. In certain embodiments, it may be desirable to change the location of the active sites. In some embodiments, it may be beneficial to locate an active site close to where data processing is occurring. In other embodiments, it may be beneficial to locate an active site where power costs are low. In further embodiments, it may be beneficial to have active sites follow daylight (i.e. be located in a place where it is daylight.). In still other embodiments, it may be beneficial to have an active site follow the night, shifting in geographic location to follow lower temperate locations to lower cooling costs.

In further embodiments, the replication sites may aid shifting of the location of the active sites. In certain embodiments, there may be two active sites connected by a virtual service layer and each active site may be replicated by one or more replication sites. In further embodiments, the current disclosure may enable a replication site and an active site to switch roles, the active site becoming the replication site and the replication site becoming the active site.

In some embodiments, the current disclosure may enable two sites to become actively linked or mirrored through a virtualization layer. In certain embodiments, replication technology may be a more efficient technology to migrate the data from the first site to the second site before making both of them actively mirror each other. In at least some embodiments, the current disclosure may allow replicating the data from the first site to the second site and enable both sites to actively mirror or have consistent data through a virtualization layer without a need for an initial synchronization between the sites using the virtualization layer.

The following definitions are employed throughout the specification and claims.

-   -   BACKUP SITE—may be a facility where replicated production site         data is stored; the backup site may be located in a remote site         or at the same location as the production site;     -   CLONE—may be a clone may be a copy or clone of the image or         images, drive or drives of a first location at a second         location;     -   DELTA MARKING STREAM—may mean the tracking of the delta between         the production and replication site, which may contain the meta         data of changed locations, the delta marking stream may be kept         persistently on the journal at the production site of the         replication, based on the delta marking data the DPA knows which         locations are different between the production and the replica         and transfers them to the replica to make both sites identical.     -   DPA—Data Protection Appliance may be a computer or a cluster of         computers, or a set of processes that serve as a data protection         appliance, responsible for data protection services including         inter alia data replication of a storage system, and journaling         of I/O requests issued by a host computer to the storage system;     -   RPA—may be q replication protection appliance, another name for         DPA.     -   HOST—may be at least one computer or networks of computers that         runs at least one data processing application that issues I/O         requests to one or more storage systems; a host is an initiator         with a SAN;     -   HOST DEVICE—may be an internal interface in a host, to a logical         storage unit;     -   IMAGE—may be a copy of a logical storage unit at a specific         point in time;     -   INITIATOR—may be a node in a SAN that issues I/O requests;     -   JOURNAL—may be a record of write transactions issued to a         storage system; used to maintain a duplicate storage system, and         to rollback the duplicate storage system to a previous point in         time;     -   LOGICAL UNIT—may be a logical entity provided by a storage         system for accessing data from the storage system;     -   LUN—may be a logical unit number for identifying a logical unit;     -   PHYSICAL STORAGE UNIT—may be a physical entity, such as a disk         or an array of disks, for storing data in storage locations that         can be accessed by address;     -   PRODUCTION SITE—may be a facility where one or more host         computers run data processing applications that write data to a         storage system and read data from the storage system;     -   SAN—may be a storage area network of nodes that send and receive         I/O and other requests, each node in the network being an         initiator or a target, or both an initiator and a target;     -   SOURCE SIDE—may be a transmitter of data within a data         replication workflow, during normal operation a production site         is the source side; and during data recovery a backup site is         the source side;     -   SNAPSHOT—may be a Snapshot may refer to differential         representations of an image, i.e. the snapshot may have pointers         to the original volume, and may point to log volumes for changed         locations. Snapshots may be combined into a snapshot array,         which may represent different images over a time period.     -   STORAGE SYSTEM—may be a SAN entity that provides multiple         logical units for access by multiple SAN initiators     -   TARGET—may be a node in a SAN that replies to I/O requests;     -   TARGET SIDE—may be a receiver of data within a data replication         workflow; during normal operation a back site is the target         side, and during data recovery a production site is the target         side;     -   WAN—a wide area network that connects local networks and enables         them to communicate with one another, such as the Internet.     -   SPLITTER/PROTECTION AGENT: may be an agent running either on a         production host a switch or a storage array which can intercept         IO and split them to a DPA and to the storage array, fail IO         redirect IO or do any other manipulation to the IO.     -   VIRTUAL VOLUME: may be a volume which is exposed to host by a         virtualization layer, the virtual volume may be span across more         than one site     -   DISTRIBUTED MIRROR: may be a mirror of a volume across distance,         either metro or geo, which is accessible at all sites.     -   BLOCK VIRTUALIZATION: may be a layer, which takes backend         storage volumes and by slicing concatenation and striping create         a new set of volumes, which serve as base volumes or devices in         the virtualization layer     -   MARKING ON SPLITTER: may be a mode in a splitter where         intercepted IOs are not split to an appliance and the storage,         but changes (meta data) are tracked in a list and/or a bitmap         and I/O is immediately sent to down the IO stack.     -   FAIL ALL MODE: may be a mode of a volume in the splitter where         all write and read IOs intercepted by the splitter are failed to         the host, but other SCSI commands like read capacity are served.     -   GLOBAL FAIL ALL MODE: may be a mode of a volume in the virtual         layer where all write and read IOs virtual layer are failed to         the host, but other SCSI commands like read capacity are served.     -   LOGGED ACCESS: may be an access method provided by the appliance         and the splitter, in which the appliance rolls the volumes of         the consistency group to the point in time the user requested         and let the host access the volumes in a copy on first write         base.     -   VIRTUAL ACCESS: may be an access method provided by the         appliance and the splitter, in which the appliance exposes a         virtual volume from a specific point in time to the host, the         data for the virtual volume is partially stored on the remote         copy and partially stored on the journal.

A description of journaling and some techniques associated with journaling may be described in the patent titled METHODS AND APPARATUS FOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION and with U.S. Pat. No. 7,516,287, which is hereby incorporated by reference.

A discussion of image access may be found in U.S. patent application Ser. No. 12/969,903 entitled “DYNAMIC LUN RESIZING IN A REPLICATION ENVIRONMENT” filed on Dec. 16, 2010 assigned to EMC Corp., which is hereby incorporated by reference.

A discussion of journal based replication may be integrated with a virtual service layer may be found in U.S. patent application Ser. Nos. 13/077,256, 13/077,262, and 13/077,266, entitled “CONSISTENT REPLICATION IN A GEOGRAPHICALLY DISPERSE ACTIVE ENVIRONMENT,” “INVERSE STAR REPLICATION,” and “NETWORKED BASED REPLICATION OF DISTRIBUTED VOLUMES,” respectively, filed on Dec. 16, 2010 assigned to EMC Corp., which is hereby incorporated by reference.

Description of Embodiments Using of a Five State Journaling Process

Reference is now made to FIG. 1, which is a simplified illustration of a data protection system 100, in accordance with an embodiment of the present invention. Shown in FIG. 1 are two sites; Site I, which is a production site, on the right, and Site II, which is a backup site, on the left. Under normal operation the production site is the source side of system 100, and the backup site is the target side of the system. The backup site is responsible for replicating production site data. Additionally, the backup site enables rollback of Site I data to an earlier pointing time, which may be used in the event of data corruption of a disaster, or alternatively in order to view or to access data from an earlier point in time.

During normal operations, the direction of replicate data flow goes from source side to target side. It is possible, however, for a user to reverse the direction of replicate data flow, in which case Site I starts to behave as a target backup site, and Site II starts to behave as a source production site. Such change of replication direction is referred to as a “failover”. A failover may be performed in the event of a disaster at the production site, or for other reasons. In some data architectures, Site I or Site II behaves as a production site for a portion of stored data, and behaves simultaneously as a backup site for another portion of stored data. In some data architectures, a portion of stored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another, or they may both be situated at a common site, local to one another. Local data protection has the advantage of minimizing data lag between target and source, and remote data protection has the advantage is being robust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN) 128, although other types of networks are also adaptable for use with the present invention.

In accordance with an embodiment of the present invention, each side of system 100 includes three major components coupled via a storage area network (SAN); namely, (i) a storage system, (ii) a host computer, and (iii) a data protection appliance (DPA). Specifically with reference to FIG. 1, the source side SAN includes a source host computer 104, a source storage system 108, and a source DPA 112. Similarly, the target side SAN includes a target host computer 116, a target storage system 120, and a target DPA 124.

Generally, a SAN includes one or more devices, referred to as “nodes”. A node in a SAN may be an “initiator” or a “target”, or both. An initiator node is a device that is able to initiate requests to one or more other devices; and a target node is a device that is able to reply to requests, such as SCSI commands, sent by an initiator node. A SAN may also include network switches, such as fiber channel switches. The communication links between each host computer and its corresponding storage system may be any appropriate medium suitable for data transfer, such as fiber communication channel links.

In an embodiment of the present invention, the host communicates with its corresponding storage system using small computer system interface (SCSI) commands.

System 100 includes source storage system 108 and target storage system 120. Each storage system includes physical storage units for storing data, such as disks or arrays of disks. Typically, storage systems 108 and 120 are target nodes. In order to enable initiators to send requests to storage system 108, storage system 108 exposes one or more logical units (LU) to which commands are issued. Thus, storage systems 108 and 120 are SAN entities that provide multiple logical units for access by multiple SAN initiators.

Logical units are a logical entity provided by a storage system, for accessing data stored in the storage system. A logical unit is identified by a unique logical unit number (LUN). In an embodiment of the present invention, storage system 108 exposes a logical unit 136, designated as LU A, and storage system 120 exposes a logical unit 156, designated as LU B.

In an embodiment of the present invention, LU B is used for replicating LU A. As such, LU B is generated as a copy of LU A. In one embodiment, LU B is configured so that its size is identical to the size of LU A. Thus for LU A, storage system 120 serves as a backup for source side storage system 108. Alternatively, as mentioned hereinabove, some logical units of storage system 120 may be used to back up logical units of storage system 108, and other logical units of storage system 120 may be used for other purposes. Moreover, in certain embodiments of the present invention, there is symmetric replication whereby some logical units of storage system 108 are used for replicating logical units of storage system 120, and other logical units of storage system 120 are used for replicating other logical units of storage system 108.

System 100 includes a source side host computer 104 and a target side host computer 116. A host computer may be one computer, or a plurality of computers, or a network of distributed computers, each computer may include inter alia a conventional CPU, volatile and non-volatile memory, a data bus, an I/O interface, a display interface and a network interface. Generally a host computer runs at least one data processing application, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host device for each logical unit exposed by a storage system in the host computer SAN. A host device is a logical entity in a host computer, through which a host computer may access a logical unit. In an embodiment of the present invention, host device 104 identifies LU A and generates a corresponding host device 140, designated as Device A, through which it can access LU A. Similarly, host computer 116 identifies LU B and generates a corresponding device 160, designated as Device B.

In an embodiment of the present invention, in the course of continuous operation, host computer 104 is a SAN initiator that issues I/O requests (write/read operations) through host device 140 to LU A using, for example, SCSI commands. Such requests are generally transmitted to LU A with an address that includes a specific device identifier, an offset within the device, and a data size. Offsets are generally aligned to 512 byte blocks. The average size of a write operation issued by host computer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks. For an I/O rate of 50 megabytes (MB) per second, this corresponds to approximately 5,000 write transactions per second.

System 100 includes two data protection appliances, a source side DPA 112 and a target side DPA 124. A DPA performs various data protection services, such as data replication of a storage system, and journaling of I/O requests issued by a host computer to source side storage system data. As explained in detail hereinbelow, when acting as a target side DPA, a DPA may also enable rollback of data to an earlier point in time, and processing of rolled back data at the target site. Each DPA 112 and 124 is a computer that includes inter alia one or more conventional CPUs and internal memory.

For additional safety precaution, each DPA is a cluster of such computers. Use of a cluster ensures that if a DPA computer is down, then the DPA functionality switches over to another computer. The DPA computers within a DPA cluster communicate with one another using at least one communication link suitable for data transfer via fiber channel or IP based protocols, or such other transfer protocol. One computer from the DPA cluster serves as the DPA leader. The DPA cluster leader coordinates between the computers in the cluster, and may also perform other tasks that require coordination between the computers, such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 are standalone devices integrated within a SAN. Alternatively, each of DPA 112 and DPA 124 may be integrated into storage system 108 and storage system 120, respectively, or integrated into host computer 104 and host computer 116, respectively. Both DPAs communicate with their respective host computers through communication lines such as fiber channels using, for example, SCSI commands.

In accordance with an embodiment of the present invention, DPAs 112 and 124 are configured to act as initiators in the SAN; i.e., they can issue I/O requests using, for example, SCSI commands, to access logical units on their respective storage systems. DPA 112 and DPA 124 are also configured with the necessary functionality to act as targets; i.e., to reply to I/O requests, such as SCSI commands, issued by other initiators in the SAN, including inter alia their respective host computers 104 and 116. Being target nodes, DPA 112 and DPA 124 may dynamically expose or remove one or more logical units.

As described hereinabove, Site I and Site II may each behave simultaneously as a production site and a backup site for different logical units. As such, DPA 112 and DPA 124 may each behave as a source DPA for some logical units, and as a target DPA for other logical units, at the same time.

In accordance with an embodiment of the present invention, host computer 104 and host computer 116 include protection agents 144 and 164, respectively. Protection agents 144 and 164 intercept SCSI commands issued by their respective host computers, via host devices to logical units that are accessible to the host computers. In accordance with an embodiment of the present invention, a data protection agent may act on an intercepted SCSI commands issued to a logical unit, in one of the following ways:

-   -   Send the SCSI commands to its intended logical unit.     -   Redirect the SCSI command to another logical unit.     -   Split the SCSI command by sending it first to the respective         DPA. After the DPA returns an acknowledgement, send the SCSI         command to its intended logical unit.     -   Fail a SCSI command by returning an error return code.     -   Delay a SCSI command by not returning an acknowledgement to the         respective host computer.

A protection agent may handle different SCSI commands, differently, according to the type of the command. For example, a SCSI command inquiring about the size of a certain logical unit may be sent directly to that logical unit, while a SCSI write command may be split and sent first to a DPA associated with the agent. A protection agent may also change its behavior for handling SCSI commands, for example as a result of an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain host device generally corresponds to the behavior of its associated DPA with respect to the logical unit of the host device. When a DPA behaves as a source site DPA for a certain logical unit, then during normal course of operation, the associated protection agent splits I/O requests issued by a host computer to the host device corresponding to that logical unit. Similarly, when a DPA behaves as a target device for a certain logical unit, then during normal course of operation, the associated protection agent fails I/O requests issued by host computer to the host device corresponding to that logical unit.

Communication between protection agents and their respective DPAs may use any protocol suitable for data transfer within a SAN, such as fiber channel, or SCSI over fiber channel. The communication may be direct, or via a logical unit exposed by the DPA. In an embodiment of the present invention, protection agents communicate with their respective DPAs by sending SCSI commands over fiber channel.

In an embodiment of the present invention, protection agents 144 and 164 are drivers located in their respective host computers 104 and 116. Alternatively, a protection agent may also be located in a fiber channel switch, or in any other device situated in a data path between a host computer and a storage system.

What follows is a detailed description of system behavior under normal production mode, and under recovery mode.

In accordance with an embodiment of the present invention, in production mode DPA 112 acts as a source site DPA for LU A. Thus, protection agent 144 is configured to act as a source side protection agent; i.e., as a splitter for host device A. Specifically, protection agent 144 replicates SCSI I/O requests. A replicated SCSI I/O request is sent to DPA 112. After receiving an acknowledgement from DPA 124, protection agent 144 then sends the SCSI I/O request to LU A. Only after receiving a second acknowledgement from storage system 108 will host computer 104 initiate another I/O request.

When DPA 112 receives a replicated SCSI write request from data protection agent 144, DPA 112 transmits certain I/O information characterizing the write request, packaged as a “write transaction”, over WAN 128 to DPA 124 on the target side, for journaling and for incorporation within target storage system 120.

DPA 112 may send its write transactions to DPA 124 using a variety of modes of transmission, including inter alia (i) a synchronous mode, (ii) an asynchronous mode, and (iii) a snapshot mode. In synchronous mode, DPA 112 sends each write transaction to DPA 124, receives back an acknowledgement from DPA 124, and in turns sends an acknowledgement back to protection agent 144. Protection agent 144 waits until receipt of such acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combines them into an aggregate “snapshot” of all write activity performed in the multiple I/O requests, and sends the snapshot to DPA 124, for journaling and for incorporation in target storage system 120. In snapshot mode DPA 112 also sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

For the sake of clarity, the ensuing discussion assumes that information is transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A from DPA 112, and performs journaling and writing to storage system 120. When applying write operations to storage system 120, DPA 124 acts as an initiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in the journal, so as to restore storage system 120 to the state it was at, at an earlier time.

As described hereinabove, in accordance with an embodiment of the present invention, LU B is used as a backup of LU A. As such, during normal production mode, while data written to LU A by host computer 104 is replicated from LU A to LU B, host computer 116 should not be sending I/O requests to LU B. To prevent such I/O requests from being sent, protection agent 164 acts as a target site protection agent for host Device B and fails I/O requests sent from host computer 116 to LU B through host Device B.

In accordance with an embodiment of the present invention, target storage system 120 exposes a logical unit 176, referred to as a “journal LU”, for maintaining a history of write transactions made to LU B, referred to as a “journal”. Alternatively, journal LU 176 may be striped over several logical units, or may reside within all of or a portion of another logical unit. DPA 124 includes a journal processor 180 for managing the journal.

Journal processor 180 functions generally to manage the journal entries of LU B. Specifically, journal processor 180 (i) enters write transactions received by DPA 124 from DPA 112 into the journal, by writing them into the journal LU, (ii) applies the journal transactions to LU B, and (iii) updates the journal entries in the journal LU with undo information and removes already-applied transactions from the journal. As described below, with reference to FIGS. 2 and 3A-3D, journal entries include four streams, two of which are written when write transaction are entered into the journal, and two of which are written when write transaction are applied and removed from the journal.

Reference is now made to FIG. 2, which is a simplified illustration of a write transaction 200 for a journal, in accordance with an embodiment of the present invention. The journal may be used to provide an adaptor for access to storage 120 at the state it was in at any specified point in time. Since the journal contains the “undo” information necessary to rollback storage system 120, data that was stored in specific memory locations at the specified point in time may be obtained by undoing write transactions that occurred subsequent to such point in time.

Write transaction 200 generally includes the following fields:

-   -   one or more identifiers;     -   a time stamp, which is the date & time at which the transaction         was received by source side DPA 112;     -   a write size, which is the size of the data block;     -   a location in journal LU 176 where the data is entered;     -   a location in LU B where the data is to be written; and     -   the data itself.

Write transaction 200 is transmitted from source side DPA 112 to target side DPA 124. As shown in FIG. 2, DPA 124 records the write transaction 200 in four streams. A first stream, referred to as a DO stream, includes new data for writing in LU B. A second stream, referred to as an DO METADATA stream, includes metadata for the write transaction, such as an identifier, a date & time, a write size, a beginning address in LU B for writing the new data in, and a pointer to the offset in the do stream where the corresponding data is located. Similarly, a third stream, referred to as an UNDO stream, includes old data that was overwritten in LU B; and a fourth stream, referred to as an UNDO METADATA, include an identifier, a date & time, a write size, a beginning address in LU B where data was to be overwritten, and a pointer to the offset in the undo stream where the corresponding old data is located.

In practice each of the four streams holds a plurality of write transaction data. As write transactions are received dynamically by target DPA 124, they are recorded at the end of the DO stream and the end of the DO METADATA stream, prior to committing the transaction. During transaction application, when the various write transactions are applied to LU B, prior to writing the new DO data into addresses within the storage system, the older data currently located in such addresses is recorded into the UNDO stream.

By recording old data, a journal entry can be used to “undo” a write transaction. To undo a transaction, old data is read from the UNDO stream in a reverse order, from the most recent data to the oldest data, for writing into addresses within LU B. Prior to writing the UNDO data into these addresses, the newer data residing in such addresses is recorded in the DO stream.

The journal LU is partitioned into segments with a pre-defined size, such as 1 MB segments, with each segment identified by a counter. The collection of such segments forms a segment pool for the four journaling streams described hereinabove. Each such stream is structured as an ordered list of segments, into which the stream data is written, and includes two pointers—a beginning pointer that points to the first segment in the list and an end pointer that points to the last segment in the list.

According to a write direction for each stream, write transaction data is appended to the stream either at the end, for a forward direction, or at the beginning, for a backward direction. As each write transaction is received by DPA 124, its size is checked to determine if it can fit within available segments. If not, then one or more segments are chosen from the segment pool and appended to the stream's ordered list of segments.

Thereafter the DO data is written into the DO stream, and the pointer to the appropriate first or last segment is updated. Freeing of segments in the ordered list is performed by simply changing the beginning or the end pointer. Freed segments are returned to the segment pool for re-use.

A journal may be made of any number of streams including less than or more than 5 streams. Often, based on the speed of the journaling and whether the back-up is synchronous or a synchronous a fewer or greater number of streams may be used.

Some information is provided for conventional continuous data protection systems having journaling and a replication splitter. A replication may set refer to an association created between the source volume and the local and/or remote target volumes, and a consistency group contains one or more replication sets. A snapshot may be the difference between one consistent image of stored data and the next. The exact time for closing the snapshot may determined dynamically depending on replication policies and the journal of the consistency group.

In synchronous replication, each write may be a snapshot. When the snapshot is distributed to a replica, it may be stored in the journal volume, so that is it possible to revert to previous images by using the stored snapshots. As noted above, a splitter mirrors may write from an application server to LUNs being protected by the data protection appliance. When a write is requested from the application server it may be split and sent to the appliance using a host splitter/driver (residing in the I/O stack, below any file system and volume manager, and just above any multipath driver (such as EMC POWERPATH), through an intelligent fabric switch, through array-based splitter.

Image Access

Herein, some information is provided for conventional continuous data protection systems having journaling and a replication splitter which may be used in one or more embodiments is provided. A replication may set refer to an association created between the source volume and the local and/or remote target volumes, and a consistency group contains one or more replication sets. A snapshot may be the difference between one consistent image of stored data and the next. The exact time for closing the snapshot may determined dynamically depending on replication policies and the journal of the consistency group.

In synchronous replication, each write may be a snapshot. When the snapshot is distributed to a replica, it may be stored in the journal volume, so that is it possible to revert to previous images by using the stored snapshots. As noted above, a splitter mirrors may write from an application server to LUNs being protected by the data protection appliance. When a write is requested from the application server it may be split and sent to the appliance using a host splitter/driver (residing in the I/O stack, below any file system and volume manager, and just above any multipath driver (such as EMC POWERPATH), through an intelligent fabric switch, through array-based splitter, such as EMC CLARiiON.

There may be a number of image access modes. Image access may be used to restore production from the disaster recovery site, and to roll back to a previous state of the data. Image access may be also to temporarily operate systems from a replicated copy while maintenance work is carried out on the production site and to fail over to the replica. When image access is enabled, host applications at the copy site may be able to access the replica.

In virtual access, the system may create the image selected in a separate virtual LUN within the data protection appliance. While performance may be constrained by the appliance, access to the point-in-time image may be nearly instantaneous. The image may be used in the same way as logged access (physical), noting that data changes are temporary and stored in the local journal. Generally, this type of image access is chosen because the user may not be sure which image, or point in time is needed. The user may access several images to conduct forensics and determine which replica is required. Note that in known systems, one cannot typically recover the production site from a virtual image since the virtual image is temporary. Generally, when analysis on the virtual image is completed, the choice is made to disable image access.

If it is determined the image should be maintained, then access may be changed to logged access using ‘roll to image.’ When disable image access is disabled, the virtual LUN and all writes to it may be discarded.

In an embodiment of virtual access with roll image in background, the system first may create the image in a virtual volume managed by the data protection appliance to provide rapid access to the image, the same as in virtual access. Simultaneously in background, the system may roll to the physical image. Once the system has completed this action, the virtual volume may be discarded, and the physical volume may take its place. At this point, the system continues to function as if logged image access was initially selected. The switch from virtual to physical may be transparent to the servers and applications and the user may not see any difference in access. Once this occurs, changes may be read from the physical volume instead of being performed by the appliance. If image access is disabled, the writes to the volume while image access was enabled may be rolled back (undone). Then distribution to storage may continue from the accessed image forward.

In some embodiments in physical logged access, the system rolls backward (or forward) to the selected snapshot (point in time). There may be a delay while the successive snapshots are applied to the replica image to create the selected image. The length of delay may depend on how far the selected snapshot is from the snapshot currently being distributed to storage. Once the access is enabled, hosts may read data directly from the volume and writes may be handled through the DPA. The host may read the undo data of the write and the appliance may store the undo data in a logged access journal. During logged access the distribution of snapshots from the journal to storage may be paused. When image access is disabled, writes to the volume while image access was enabled (tracked in the logged access journal) may be rolled back (undone). Then distribution to storage may continue from the accessed snapshot forward.

Disable image access may mean changes to the replica may be discarded or thrown away. It may not matter what type of access was initiated, that is, logged or another type, or whether the image chosen was the latest or an image back in time. Disable image access effectively says the work done at the disaster recovery site is no longer needed.

Virtual Service Layer

Typical server environments have one or more hosts access storage. Conventionally, some of the hosts may be virtual hosts or virtual machines. Generally, each virtual machine or host has a LUN or logical unit corresponding to storage space it may access. Typically, this LUN corresponds to a portion of one or more physical disks mapped to the LUN or logical drive.

Conventional Server virtualization products may have developed the capability to execute migrations of virtual machines, the underlying storage, or both to address load balancing and high availability requirements with certain limitations. Typically, conventional solutions usually require disruptive failover (i.e. failure of one site to transfer the processes to the back-up site), merged SANs, and do not work with heterogeneous products. Thus, in typical systems, if a Virtual Machine were migrated to another environment, such as a server at another location outside of a site, the virtual machine would no longer have read write access to the LUN. However, it is desirable to be able to migrate a virtual machine and have it still be able to have read write access to the underlying storage.

In certain embodiments of the instant disclosure, storage resources are enabled to be aggregated and virtualized to provide a dynamic storage infrastructure to complement the dynamic virtual server infrastructure. In an embodiment of the current invention, users are enabled to access a single copy of data at different geographical locations concurrently, enabling a transparent migration of running virtual machines between data centers. In some embodiments, this capability may enable for transparent load sharing between multiple sites while providing the flexibility of migrating workloads between sites in anticipation of planned events. In other embodiments, in case of an unplanned event that causes disruption of services at one of the data centers, the failed services maybe restarted at the surviving site with minimal effort while minimizing recovery time objective (RTO).

In some embodiments of the current techniques the IT infrastructure including servers, storage, and networks may be virtualized. In certain embodiments, resources may be presented as a uniform set of elements in the virtual environment. In other embodiments of the current techniques local and distributed federation is enabled which may allow transparent cooperation of physical data elements within a single site or two geographically separated sites. In some embodiments, the federation capabilities may enable collection of the heterogeneous data storage solutions at a physical site and present the storage as a pool of resources. In some embodiments, virtual storage is enabled to span multiple data centers

In some embodiments, virtual storage or a virtual storage layer may have a front end and a back end. The back end may consume storage volumes and create virtual volumes from the consumed volumes. The virtual volumes may be made up of portions or concatenations of the consumed volumes. For example, the virtual volumes may stripped across the consumed volumes or may be made up of consumed volumes running a flavor of RAID. Usually, the front-end exposes these volumes to hosts.

An example embodiment of a virtual service layer or virtual service appliance is EMC Corporation's Vplex®. In some embodiments of the instant disclosure, a storage virtualization appliance has a back-end exposes LUNs to hosts and a front-end which talks to storage arrays, which may enable data mobility. In certain embodiments, storage may be added or removed from the virtual service layer transparently to the user

In most embodiments, the virtual service layer enables cache coherency. Thus, in certain embodiments of the current techniques, the storage volumes, in a virtualized server environment, which comprise the encapsulation of a virtual machine may be coherently co-located in two sites, enabling simultaneous, local access by the virtual machine regardless of whether the virtual machine is located on the local or remote site. In other embodiments, cooperative clustering of the virtualization server nodes may allow for active/active, concurrent read/write access to one or more federated storage devices across the sites. In further embodiments, concurrent access may occur even if the data has not yet been fully copied between the two sites. In at least some embodiments of the current techniques, it is enabled to reference the source copy in this case, preserving seamless, continuous operation.

In certain embodiments of the current disclosure, movement of the virtual machines between the two sites is facilitated. In some embodiments, LUN level access is active/active, any single virtual machine may execute on only one node of the cluster. In further embodiments, enabling of migration of virtual machine instances may enable the migration of the I/O load (specifically read workloads) to storage devices located in the site where the active node resides for any given virtual machine.

In some embodiments of the current techniques, the ability to migrate a VM may be enabled through the use of one or more federated virtual volume. In certain embodiments, a virtual machine or application may communicate through a network with a module which presents virtual volumes to the application or virtual machine. In further embodiments the network may be a SAN. In at least some embodiments, this module may provide a level of abstraction between the storage and the requests for storage made by a virtual machine or other application. In these embodiments, the module may map the logical drive presented to the VM or application to the storage device. In certain embodiments, the module may be transparent to the storage request, the application or VM functioning as it is accessing a logical drive across a network. In other embodiments the network may be a SAN. In other embodiments, regardless of location of the VM, the VM may attempt to reach the LUN provided by the module, which may map the VM request to the appropriate storage.

In some embodiments of the current invention, a clustering architecture enables servers at multiple data centers to have concurrent read and write access to shared block storage devices. In alternative embodiments of the current invention, load sharing between multiple sites while providing the flexibility of migrating workloads between sites in anticipation of planned events such as hardware maintenance is enabled. In further embodiments, in case of an unplanned event that causes disruption of services at one of the data centers, the failed services may be quickly and easily restarted at the surviving site with minimal effort.

In most embodiments, the module may communicate with a second module at the second site to facilitate the one or more federated logical drive. In some embodiments, if a VM were to be moved from the first site to the second site the VM would attempt to access storage through the second module. In most embodiments, the move would be transparent to the VM as it would simply reach out to access the storage and the module on the second site would re-direct the request to the storage on the second site. In some embodiments, the module on the second site would direct the request to the data on the second site. In some embodiments, the storage may be kept in sync using a mirror, the VM may access a current version of the data, regardless of on which site the VM is located. The modules at the first and second site may be in communication with each other.

In some embodiments, disparate storage arrays at two separate locations may be enabled to appear as a single, shared array to application hosts, allowing for the easy migration and planned relocation of application servers and application data, whether physical or virtual. In other embodiments, effective information distribution by sharing and pooling storage resources across multiple hosts may enabled. In further embodiments, manage of virtual environment may be enabled to transparently share and balance resources across physical data centers, ensure instant, realtime data access for remote users, increase protection to reduce unplanned application outages, and transparently share and balance resources within and across physical data centers.

In further embodiments, concurrent read and write access to data by multiple hosts across two locations may be enabled. In other embodiments, realtime data access to remote physical data centers without local storage may be enabled. In some embodiments, the virtual service layer may be implemented by EMC's VPLEX or the like.

Refer to the example embodiment of a virtual service layer of FIG. 3. In the embodiment of FIG. 3, there are two sites 310, 350. Each site has a respective VM space or a space able to run virtual machine, 315, 355, SANs, 320, 330, 360, and 375 and storage 335, 380, respectively. The two sites also have a virtual service layer 385, which presents virtual volumes 325. The synchronization 390 of the storage 335 is provided by the virtual service layer 385. In the embodiment of FIG. 3, the same virtual volume may be exposed via the virtual service layer 385. This volume may be kept synchronized so that any VM in VM Space 315 or VM in VM Space 355 accesses the same virtual volume with the same data regardless of in which VM Space, 315, 355, the VM resides.

In some embodiments of the current disclosure, replication and data mobility may be enabled at difference geographic sites. In certain embodiments, this may be enabled by cache coherency functionality. In at least some embodiments, the cache coherency may enable data to be consistent over large distances and be able to be accessed at both geo sites. In a particular embodiment, there may be two geo sites. In this embodiment, if a read is performed on an area of the storage that does not belong to the local site, the read may be delayed and the read may be performed on the remote site. In this embodiment, if a read is performed on an area owned by the local site, then the read may be performed on the local site.

In other embodiments, the geo sites may enforce a write order fidelity mechanism (WOFM) by periodically quiescing or stopping the storage and ensure that the replicated data is consistent. In these embodiments, a checkpoint may be created at each site. In these embodiments, this checkpoint may be transmitted to the other site. In these embodiments, the other site may flush this checkpoint in order to ensure it has the data as the other site. In these embodiments, only consistent data may be written to the other site. In these embodiments, if a site crashes, then both sites are ensured to have a point in time, where both sites have the same data.

A discussion of some types of virtual storage may be found in U.S. Pat. No. 7,206,863, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND PROVIDING VIRTUALIZATION OF RESOURCES IN SUCH A NETWORK” issued on Apr. 17, 2007, to EMC Corp, U.S. Pat. No. 7,770,059, entitled “FAILURE PROTECTION IN AN ENVIRONMENT INCLUDING VIRTUALIZATION OF NETWORKED STORAGE RESOURCES” issued on Aug. 3, 2010, to EMC Corp, U.S. Pat. No. 7,739,448, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND PROVIDING VIRTUALIZATION OF RESOURCES IN SUCH A NETWORK” issued on Jun. 15, 2010, to EMC Corp, U.S. Pat. No. 7,739,448, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND PROVIDING VIRTUALIZATION OF RESOURCES IN SUCH A NETWORK USING ONE OR MORE ASICS” issued on Nov. 17, 2009, to EMC Corp, U.S. Pat. No. 7,620,774, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND PROVIDING VIRTUALIZATION OF RESOURCES IN SUCH A NETWORK USING ONE OR MORE CONTROL PATH CONTROLLERS WITH AN EMBEDDED ASIC ON EACH CONTROLLER” issued on Nov. 17, 2009, to EMC Corp, U.S. Pat. No. 7,225,317, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND FOR MANAGING SCALABILITY OF VOLUMES IN SUCH A NETWORK” issued on May 29, 2007, to EMC Corp, U.S. Pat. No. 7,315,914, entitled “SYSTEMS AND METHODS FOR MANAGING VIRTUALIZED LOGICAL UNITS USING VENDOR SPECIFIC STORAGE ARRAY COMMANDS” issued on Jan. 1, 2008, to EMC Corp, and U.S. Pat. No. 7,216,264, entitled “SYSTEM AND METHOD FOR MANAGING STORAGE NETWORKS AND FOR HANDLING ERRORS IN SUCH A NETWORK” issued on May 8, 2007, to EMC Corp, all of which are hereby incorporated by reference. A discussion of mirroring may be found in U.S. Pat. No. 7,346,805, entitled “PROTECTION OF MIRRORED DATA” issued on Mar. 18, 2008 to EMC Corp, which is hereby incorporated by reference.

Journal Based Replication in a Virtual Storage Layer with a Splitter

In some embodiments of the instant disclosure, a virtual service layer may have journal based replication. In certain embodiments of the instant disclosure, data consistency between different sites serviced by a virtual service layer may be ensured. In most embodiments, one or more splitter may be integrated into the virtual service layer.

Refer now to the example embodiment of FIG. 4. In the embodiment of FIG. 4, an I/O splitter has been inserted into the Virtual Service Layer. In these embodiments, the splitter 427 may split I/O occurring at the virtual service layer 485. The I/O Splitter may be made up of one or more splitters in each node at each site. In the example embodiment of FIG. 4, there is one node at each site 410 and 450 and there is one splitter 428, 429, respectively, for each site 410, 450.

Refer now to the exemplary embodiment of FIG. 5. The example embodiment of FIG. 5 illustrates a sample virtual service layer divided into underlying layers. In FIG. 5, the Virtual Service Layer 510 has a front-end SCSI target 515 that may be exposed to a host. In FIG. 5, there is also a cache 520. In some embodiments the cache may be a write-through cache. In other embodiments it may be a write-order fidelity cache. In FIG. 5, there is also a virtual volume 530 also exposed to a host or several hosts. The virtual volume may be supported by a distributed mirror 540. A distributed mirror may be a mirror which gives a remote active copy of the volume that is mirrored at another site. The distributed mirror enables mirroring between two geographically disparate sites. There may be a splitter 545 inserted between the virtual volume 530 and the block virtualization 550. As well, there may also be storage volume 555 and a back-end SCSI initiatior 560.

Refer now to the example embodiment of FIG. 6. In this example embodiment, splitter 615 communicates with recovery appliance 625. In some embodiments, the appliance may alternatively be set of process running inside the virtual service cluster. Splitter 615 splits the I/O in the virtual service layer and sends the I/O to recovery appliance 625 and to the block virtualization layer. The recovery appliance 625 may keep journal 640 of the I/O and may also keep a repository volume 645, for persistent configuration, and may keep a copy of the production image 635 serviced by the Virtual service layer 610. Journal 640 and repository 645 volumes may be served from virtual service layer 610 or from a backend array directly. The appliance may also transfer the data to remote site 620 and create a remote copy of the data in a different storage array.

Refer now to the example embodiment of FIG. 7. In the example embodiment of FIG. 7, sites 710 and 720 have virtual service layers 715, 725 and each VSL has a splitter, 730, and 735. The Virtual Volumes or production volumes 750 and 752 are distributed mirrors and kept consistent across sites 710, 720. Each IO performed at site 710 may be transmitted to site 720. In this example, both splitters, 730, 735 may intercept the same I/O and the same I/O may be intercepted twice. At site 710 and 720, there may be multiple directors such as directors 727 and 728. A director may be a construct that exposes the LUNs in the storage. Two directors may form a construct called an engine. Each director 727, 728 in VSL 715 may have a splitter 730, 731. All the directors at each site may expose the LUNs to hosts, the host may send each IO to one of the directors (for load balancing IOs to the same LUN may be sent to different directors), the IO arriving at a director may be intercepted by the splitter running at the same director, if the volume is a distributed mirror, the IO may also be sent to another director at the mirror site and intercepted also by the splitter running at the other director.

Refer now to the example embodiment of FIG. 8. In the embodiment of FIG. 8, there are two sites, 810 and 850 which may be geographically disperse. Each site may have a virtual service layer and the I/O processed at sites 810, 850 may be split by splitter 815. Site 810 may have a volume 830, a CDP copy 835 (volume 835 contains a full copy of volume 830, and with the journal together, provides a continuous protection for a window of time), and a journal 840. The volume 830 and the journal 840 may be local to site 810 and may not be distributed to site 850 by the virtualization layer. Since there are no appliances at site 850, volume 860 may not be replicated so IOs arriving at splitter 855 for volume 860 may be ignored by the splitter and sent to the block virtualization layer.

Refer now to the example embodiment of FIG. 9. In the embodiment of FIG. 9, there may be a recovery appliance 925, 985 at each site 910, 950. Each site, 910, 950, has a distributed mirror volume 930, 960 respectively, CDP Replica copy 935, 965, Journal 940, 970, and repository 945, 1075. In the embodiment of FIG. 9, if an I/O is written to site 910, the I/O may be split by both splitter 915 and 955. In this embodiment, the VSL 912, 952 keep the mirrored volume 930, 960 consistent and the I/O written at site 910 gets transferred to site 950. The I/O may then get transferred to CDP 935 as well as to CDP 965. In this embodiment, the replication appliances 925 and 985 may not be aware of each other. Volumes 935 and 965 may be local volumes and not mirrored by the VSL, and may be completely independent copies of the distributed volume.

In this embodiment, if site 910 is down, the connection between sites 910 and 950 is broken and site 950 may continue to function, and replicate the data to replica copy 965. When site 910 is no longer down, VSL 912, 952 may work to restore the mirror and no snapshots may be taken by the RPAs 925, on site 950 as the mirror remained active snapshots may continue to be close during the restoration of volume 930.

Refer now to the sample embodiment of FIGS. 9 and 10 which illustrates a particular functionality of the sites. In the embodiments of FIGS. 9 and 10, a splitter such as any splitter 915 in FIG. 9 may intercept the I/O received at site 910 (step 1010). It may be determined if the splitter 915 is splitting I/O for the volume to which the IO is sent (step 1015). If the splitter is splitting I/O, the I/O may be sent to the RPA 925 (step 1020). When IO is acknowledged (step 1030), IO is sent to block virtualization layer (step 1040), if splitter is not splitting IOs, the IO is sent directly to the block virtualization layer and ignored by the splitter. In some embodiments IO may be send to both appliance and storage virtualization layer in parallel.

Active-Replication Switch

Refer now to the example embodiments of FIGS. 11 and 14. In the example embodiment of FIG. 11, Site A 1110 is connected to Site B 1115 by VSL 1120, and volumes 1118/1119 are expose by the VSL as one active/active volume. In this embodiment, Virtual Service layer may provide the sites with a method for synchronizing data and data access between the sites to enable both sites to have the same set of data, i.e. volumes 1118 and 1119 have the same data. The VSL may expose the same volume as an active volume to hosts at both sites, i.e. host at site A may write to volume 1118 and host at site B may write to volume 1119. Both host see the volume as the same entity, in this embodiments the same SCSI entity, and the VSL maintains cache coherency between the volumes, so that the volumes behave as one active/active volume. In this embodiment, it is desired to move sites A 1110 and site B 1115 from a virtual service layer method of synchronization to asynchronous replication. This change makes volume 1119 a replica of volume 1118 instead of being one logical volume. At Site A 1110 splitter 1112 is attached to volume 1118 and at Site B splitter 1117 is attached to volume 1119 (step 1404). Splitter 1112 and 1117 are set to tracking mode and track IO changes that arrive to volume 1118 and 1119 at sites A 1110 and B 1115 respectively. In certain embodiments, active/active replication may require more resources than asynchronous replication and may not allow journaling while in active/active replication, thus switching to asynchronous replication may allow usage of fewer resources.

Refer now to the example embodiments of FIGS. 12 and 14. VSL moves to degraded mode and stops accepting new IOs for volume 1219 from Site B (step 1410). Site A 1210 accepts IOs to volume 1218 while site B 1215 accepts no new IO and becomes passive (1415). Data cached by VSL 1220 is flushed from site A 1210 to site B 1215 and data from site B 1215 is flushed to Site A 1210 (step 1420) (in some embodiments, if the VSL is synchronous there may not be a need for flushing). VSL 1220 connecting site 1210 to site 1215 is broken (Step 1440). Refer now to the example embodiments of FIGS. 13 and 14.

Splitter 1312 starts splitting new IOs arriving to volume 1318 to data protection appliance 1325 connected to site A 1310 and IO is split by splitter 1312 to data protection appliance 1325. Data protection appliance sends IO to data protection appliance 1330, which is connected to site B 1315. Data Protection appliance 1330 communicates IO to Site B 1315 to enable asynchronous replication between sites 1310 and site 1315 (site 1450) and applies the IOs arriving to site B 1315 to the journal and from the journal to volume 1319. The changes tracked by the splitters may need to be synchronized between sites A and B. In certain embodiments, the methodology in FIGS. 11-14 may be applied to a set of volumes transitioning a set of volumes from replication using a VSL to replication using replication appliances.

Refer to the example embodiments of FIGS. 15, 16, and 17. In the example embodiment of FIG. 15, replication of volume 1518 is occurring from Site A 1510 through splitter 1512 to data protection appliance 1525. Data protection appliance 1525 sends IO to data protection appliance 1520, which synchronizes the data to site B 1515 and applies the data arriving to the journal and then to target volume 1519. In certain embodiments, data synchronization may be changed from using asynchronous replication to active/active (either synchronous or asynchronous active/active replication) through the use of a virtual service layer. Making volumes 1518 and 1519 behave as one volume may allow hosts to access what functions as the same volume at both sites. While replicating asynchronously volumes 1518 and 1519 may have the same volume identification, such as SCSI identities, or different identification, but the virtualization layer exposes an active/active volume with the same identity at both sites. In these embodiments, the identity of the remote volume is made identical to the production volume via VSL 1520 (if they are not already identical) (step 1701). Virtual service layer 1520 is created in a broken mode (i.e. not actively replicating) as illustrated in FIG. 15 (step 1705), between volumes 1518 and 1519. In these embodiments, virtualization layer 1520 at site A 1510 is tracking the changes arriving to site A 1510. Tracking bitmap 1527 is initialized as an empty (step 1710). IOs arriving to virtualization layer 1520 are split to DPA 1525 (step 1712). Virtualization layer 1520 is not replicating IO and is tracking IO in bitmap 1527 (step 1714). Site B 1515 receives IOs from DPA 1530. A bookmark is created for the replication layer (step 1720). The bookmark is applied to site B 1515 (step 1740), i.e. all data which arrived until the bookmark was created is applied to replica volume 1519. Replication via DPA 1525 and SPA 1530 is stopped (step 1745). VSL 1620 is notified to recover (step 1750). VSL 1620 synchronizes changes received since it was created as a broken virtualization layer which were tracked by the bitmap (step 1755).

Refer now to the example embodiment of FIG. 18. FIG. 18 represents a simplified alternative illustration of sites and replication appliances similar to those of the embodiments of FIG. 6, 8, or 9. In the example embodiment of FIG. 18, Site A 1810 and Site B 1815 are active/active sites and data between them is maintained by a virtualization layer, and site A is being replicated to Site D 1820 using some replication technique. Site B 1815 is be replicated to site C 1830. Site A 1810 and Site B 1815 are connected via a virtual service layer VSL 1820.

In certain embodiments, it may be desired to replace the site which are active/active and the sites which are replicating the data of the active/active sites. In some embodiments, maintaining a volume as an active/active volume may require more resources than asynchronous replication. In at least some embodiments, there may not be enough resources for all sites to be active. In further embodiments, the system may allow the user to choose two sites which can be active/active and two which hosts can write at each point in time. In still further embodiments, the user may desire the active sites to shift at different times, such as when power costs shift at different locations. In at least some embodiments, the active sites may be shifted as indicated, such as following the sun (which may map to power costs). In other embodiments, the allocation of active sites may change every few hours according to the location of the sites. In alternative embodiments, the allocation of active sites may change according to time zones where the time is during the working hours.

Refer now as well to the example embodiments of FIG. 19 and FIG. 20. FIG. 19 is a method that may be applied to transition FIG. 18 to FIG. 20 to have, instead of having two sites which are active/active, one active site replicating to two sites and having cascaded replication from one replica site to another site. In these embodiments, a replication connection from site B to site A is created in a similar manner to that of FIGS. 11-14. VSL 1820 stop accepting new IOS at site A 1810 (step 1900). Splitter 2017 at site B 2015 continues splitting IOs to replication appliance 2018 at site B 2015 which replicated IOs to the site C 2030 (step 1910). Replication appliance 2018 at site B 2015 starts tracking changes in a delta marker stream, which is tracking changes between site B 2015 and site A 2010. Virtualization layer 2020 is sending new IO arriving to site B 2015 to site A 2010 and splitter 2012 at site A 2010 splits these IOs to DPA 2013 at site A 2010 which replicates the changes to site D 2020 (step 1920). Virtualization layer 2020 is broken and removed (step 1930). Replication starts from site B 2015 to site A 2010 (synchronizing the changes which were intercepted and tracked and the marking stream between site B 2015 and site A 2010) (step 1940). IOs arriving to site A 2010 by replication appliance 2013 at site A 2010 and written to storage at site A 2010 are also replicate to site D 2020 (step 1950) (cascaded replication). Site B 2015 is active and accepting IOs for the volumes.

Refer now to the example embodiments of FIGS. 21, 22 and 23. The replication connection of FIG. 21 between site B 2115 and site C 2130, may be stopped (step 2305), VSL 2120 is created between sites 2115 and 2130. VSL 2120 may be used to make site B 2115 and site C 2130 active/active. In these embodiments, VSL 2120 is created (in some embodiment the VSL is created as described in FIGS. 15-18) (step 2320). Host may access the data at sites B 2215 and C 2230 which are active/active, data arriving to the volume exposed by VSL 2120 at either of the sites is replicated to site A 2110 and from site A 2110 data is replicated to site D 2120.

Replication between site A 2230 and site D 2220 is stopped. Replication between site C 2230 and site D 2220 is started using Splitter 2132 and DPA 2155 and DPA 2150 (step 2340). This may be performed without a full sweep synchronization as the differences between site C 2230 and Site B 2215. The differences between Site D 2220 and site A 2210 and the differences between site A 2210 and site B 2215 may be found in the marking streams maintained by the replication appliances tracking the replication. In these embodiments, site B 2215 and Site C 2230 are active/active and the changes tracked by splitter 2232 at site C 2230 include the changes between site B 2215 and site C 2230 if the active/active layer flushes the cached data after splitter starts tracking new IOs. The techniques outlined in FIGS. 18-23 provide an example embodiment of changing the set of active/active site and the set of replica sites without requirement of and full resynchronization and without disruption. In other embodiments, the current disclosure may enable changing replication connection to active/active connection, changing active/active connection to replication connection. In certain embodiments, the current techniques may enable starting replication from one site to a new target without full synchronization but reading the differences between sites, and allowing seamless change from any configuration to any configuration.

The methods and apparatus of this invention may take the form, at least partially, of program code (i.e., instructions) embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, random access or read only-memory, or any other machine-readable storage medium. When the program code is loaded into and executed by a machine, such as the computer of FIG. 24, the machine becomes an apparatus for practicing the invention. When implemented on one or more general-purpose processors, the program code combines with such a processor 2403 to provide a unique apparatus that operates analogously to specific logic circuits. As such a general purpose digital machine can be transformed into a special purpose digital machine. FIG. 25 shows Program Logic 2534 embodied on a computer-readable medium 2530 as shown, and wherein the Logic is encoded in computer-executable code configured for carrying out the reservation service process of this invention and thereby forming a Computer Program Product 2500. The logic 2534 may be the same logic 2440 on memory 2404 loaded on processor 2403. The program logic may also be embodied in software modules, as modules, or as hardware modules. The program logic may be executed by virtual processors, virtual machines, and virtual servers.

The logic for carrying out the method may be embodied as part of the aforementioned system, which is useful for carrying out a method described with reference to embodiments shown in, for example, FIG. 1 and FIG. 2. For purposes of illustrating the present invention, the invention is described as embodied in a specific configuration and using special logical arrangements, but one skilled in the art will appreciate that the device is not limited to the specific configuration but rather only by the claims included with this specification.

Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present implementations are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

In reading the above description, persons skilled in the art will realize that there are many apparent variations that can be applied to the methods and systems described. Thus it may be appreciated that, in addition to data replication systems, the optimal journaling policy of the present invention has widespread application to journaling systems including database systems and version control systems.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific exemplary embodiments without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. 

What is claimed is:
 1. A system for multiple site data replication, the system comprising: a set of sites, wherein each site of the set of sites has a volume; a virtual service layer (VSL) enabled to be coupled to two sites of the set of sites, wherein the VSL presents a single volume at each of the two sites, wherein the VSL enables concurrent read/write access to the single volume at each of the two sites coupled to the VSL, and wherein the VSL synchronizes data of the single volume using a synchronization technique and the volumes of each of the two sites of the sets of sites; and computer-executable logic operating in memory, wherein the computer-executable program logic is configured to enable execution of: presenting at the two sites of the set of sites, via the VSL, a single volume, wherein a third site of the set of sites not coupled to the VSL is enabled to replicate the data of the single volume presented by the VSL to the third site using a replication technique, and wherein the replication technique uses one or more splitters to create a copy of IO sent to the single volume, regardless of to which of the sites coupled to the VSL the IO was sent; and enabling the system to transparently shift between which two sites of the set of sites are coupled by the VSL and which site of the set of sites, other than the sites coupled by the VSL, replicates the single volume presented by the VSL.
 2. The system of claim 1, wherein each site of the set of sites comprises a splitter and a replication device, wherein the logic is further configured to enable: stopping synchronization between two sites using the VSL; uncoupling the two sites from the VSL; stopping replication between the single volume and the third site; coupling the third site with a first site of the two sites with the VSL; exposing, via the VSL, the single volume at the first site and the third site; and replicating IO sent to the single volume to a second site of the two sites using the replication technique.
 3. The system of claim 2, wherein establishing a VSL comprises: creating the VSL in a state where the VSL is not synchronizing data of the single volume, creating an empty VSL bitmap; communicatively coupling two sites of the set of sites via the VSL; modifying the identity of the volumes of the two sites using the VSL to have the same identity; tracking IO changes to the single volume of the two sites in a VSL bitmap after creation of the VSL; and enabling active/active access to the single volume via the VSL.
 4. The system of claim 3, wherein the computer-executable program logic is further configured to enable execution of: creating a bookmark for the replication technique; and stopping replication of the single volume using the replication technique.
 5. The system of claim 3, wherein stopping synchronization using the VSL comprises: tracking changes at the splitters for the volumes corresponding to the single volume of the VSL; stopping acceptance of IO to the single volume at a second site of the two sites by the VSL; and breaking the VSL connection between the two sites.
 6. The system of claim 5, wherein starting replication using the replication technique comprises: starting replication from the first site of the two sites to the second site of the two sites using the splitter of first site of the two sites and replication appliances of the first site and the second site; and synchronizing the changes tracked by the splitters of the two sites.
 7. The system of claim 1 wherein the computer-executable program logic is further configured to enable execution of: stopping replicating from a first site to a second site of the set of sites; and enabling replication from a third site of the set of sites to the second site of the set of sites by collecting a set of differences between the third site of the set of sites and the first site of the set of sites and the differences between the first site of the set of sites and the second site of the set of sites.
 8. A computer implemented method for multiple site data replication, the system method: enabling a virtual service layer (VSL) to be coupled to two sites of a set of sites, wherein each site of the set of sites has a volume; wherein the VSL presents a single volume at each of the two sites, wherein the VSL enables concurrent read/write access to the single volume at each of the two sites coupled to the VSL, and wherein the VSL synchronizes data of the single volume using a synchronization technique and the volumes of each of the two sites of the sets of sites; presenting at the two sites of the set of sites, via the VSL, a single volume, wherein a third site of the set of sites not coupled to the VSL is enabled to replicate the data of the single volume presented by the VSL to the third site using a replication technique, and wherein the replication technique uses one or more splitters to create a copy of IO sent to the single volume, regardless of to which of the sites coupled to the VSL the IO was sent; and enabling the system to transparently shift between which two sites of the set of sites are coupled by the VSL and which site of the set of sites, other than the sites coupled by the VSL, replicates the single volume presented by the VSL.
 9. The method of claim 8, wherein each site of the set of sites comprises a splitter and a replication device wherein the method further comprises: stopping synchronization between two sites using the VSL; uncoupling the two sites from the VSL; stopping replication between the single volume and the third site; coupling the third site with a first site of the two sites with the VSL; exposing, via the VSL, the single volume at the first site and the third site; and replicating IO sent to the single volume to a second site of the two sites using the replication technique.
 10. The method of claim 9 wherein establishing a VSL comprises: creating the VSL in a state where the VSL is not synchronizing data of the single volume, creating an empty VSL bitmap; communicatively coupling two sites of the set of sites via the VSL; modifying the identity of the volumes of the two sites using the VSL to have the same identity; tracking IO changes to the single volume of the two sites in a VSL bitmap after creation of the VSL; and enabling active/active access to the single volume via the VSL.
 11. The method of claim 10, further comprising: creating a bookmark for the replication technique; and stopping replication of the single volume using the replication technique.
 12. The method of claim 10, further comprising: stopping acceptance of IO at the single volume at a second site of the two sites by the VSL; and breaking the VSL connection between the two sites.
 13. The method of claim 10, wherein starting replication using the second replication technique comprises: starting replication from the first site of the two sites to the second site of the two sites using the splitter of first site of the two sites and replication appliances of the first site and the second site; and synchronizing the changes tracked by the splitters of the two sites.
 14. A computer program product comprising: a non-transitory computer readable medium encoded with computer executable program code for replication of data, the code configured to enable the execution of: enabling a virtual service layer (VSL) to be coupled to two sites of a set of sites, wherein each site of the set of sites has a volume, wherein the VSL presents a single volume at each of the two sites, wherein the VSL enables concurrent read/write access to the single volume at each of the two sites coupled to the VSL, and wherein the VSL synchronizes data of the single volume using a synchronization technique and the volumes of each of the two sites of the sets of sites; presenting at the two sites of the set of sites, via the VSL, a single volume, wherein a third site of the set of sites not coupled to the VSL is enabled to replicate the data of the single volume presented by the VSL to the third site using a replication technique, and wherein the replication technique uses one or more splitters to create a copy of IO sent to the single volume, regardless of to which of the sites coupled to the VSL the IO was sent; and enabling the system to transparently shift between which two sites of the set of sites are coupled by the VSL and which site of the set of sites, other than the sites coupled by the VSL, replicates the single volume presented by the VSL.
 15. The computer program product of claim 14, wherein site of the set of sites comprises a splitter and a replication device wherein the code is further configured to enable: stopping synchronization between two sites using the VSL; uncoupling the two sites from the VSL; stopping replication between the single volume and the third site; coupling the third site with a first site of the two sites with the VSL; exposing, via the VSL, the single volume at the first site and the third site; and replicating IO sent to the single volume to a second site of the two sites using the replication technique.
 16. The computer program product of claim 15, wherein establishing a VSL comprises: creating the VSL in a state where the VSL is not synchronizing data of the single volume, creating an empty VSL bitmap; communicatively coupling two sites of the set of sites via the VSL; modifying the identity of the volumes of the two sites using the VSL to have the same identity; tracking IO changes to the single volume of the two sites in a VSL bitmap after creation of the VSL; and enabling active/active access to the single volume via the VSL.
 17. The computer program product of claim 15, wherein the code is further configured to enable: creating a bookmark for the replication technique; and stopping replication of the single volume using the replication technique.
 18. The computer program product of claim 15, wherein the code is further configured to enable: stopping acceptance of IO at the single volume at a second site of the two sites by the VSL; and breaking the VSL connection between the two sites.
 19. The computer program product of claim 15, wherein starting replication using the replication technique comprises: starting replication from the first site of the two sites to the second site of the two sites using the splitter of first site of the two sites and replication appliances of the first site and the second site; and synchronizing the changes tracked by the splitters of the two sites. 